UDP proxy coordinator ping and forwarding notification fixes

First fix removes superfluous GUID sent in the payload, which caused out-of-bounds read in UDPProxyCoordinator::OnPingServersReplyFromClientToCoordinator(Packet *packet) and crash on the client side.

Second fix restores the correct GUID sent with the UDP proxy forwarding notification. Originally we sent target client GUID to the target client which didn't make any sense.